1. Field of the Invention
The invention relates to an apparatus for contactless sealing of an opening against emerging or entering gas by means of at least one barrier gas jet.
2. Description of the Prior Art
In plants and apparatuses in which passing materials or products are subjected to gas streams in closed chambers the sealing of the inlet and exit openings of said chamber represents a problem. This is true in particular when the goods to be treated have sensitive surfaces so that a contact sealing, for example by means of a fabric curtain or an engaging brush or roller, is out of the question. In such a case contactless sealings must be provided as can be realized only with jet curtains.
In such contactless sealing in many cases it must additionally be ensured that mixing of the outer atmosphere with the atmosphere within the chamber to be sealed is avoided. This is particularly important when, for example, in protective-gas-operated plants or in driers the entry of atmospheric oxygen must be avoided at all costs for process or safety reasons.
However, due to the turbulence generated by a jet a jet stream always leads to intense mixing between the jet curtain on the one hand and the outer atmosphere on the other so that the conventional apparatuses for contactless sealing do not meet the requirements made.
Various publications deal with jet seals for compensating a pressure difference, i.e. for avoiding large-area flowing through of the opening to be sealed due to the pressure difference between the environment and the interior space to be sealed. A fundamental investigation has been carried out in a dissertation written at The Technical University of North-Rhine Westfalia in Aachen in 1983 by H. W. Kuster. It was found that although by means of a slit jet inclined with respect to the pressure gradient or by means of a corresponding arrangement of jet openings, which in effect also produce a slit jet, a pressure difference can be compensated; due to the already mentioned jet mixing, however, a turbulent exchange always occurs between the space to be sealed and the environment and this cannot be tolerated for many uses. As these investigations show, a concentration sealing which would prevent the exchange between the outer atmosphere and the interior of the chamber can be achieved with a jet; however, for this purpose slit jets are necessary having exit nozzle openings which are so dimensioned that the edge face of the opening to be sealed disposed opposite the slit nozzle is still subjected fully to the core jet. This requires either very narrow openings or relatively wide jets which in turn lead to a high gas consumption.
A further disadvantage resides in that with the slit jet a part of the amount of gas ejected from the slit nozzle (which in this case corresponds to the plant atmosphere) is blown into the outer atmosphere and mixed therein. This is, however, for safety reasons along usually not permitted in apparatuses in which, for example, dangerous or noxious gases circulate within a chamber to be sealed.